Such a gas bag module offers advantages in particular restraint situations, such as for example a non-optimum restraint position of a vehicle occupant. As the closest prior art, US 2004/0051286 A1 discloses a gas bag module in which a distance between the vehicle occupant and a housing of the gas bag module is determined by means of limiting straps in an unfolding phase of the gas bag. With a sufficiently great distance, the limiting straps are tightened and discharge openings which are provided on the module side are closed. In another case, i.e. when the occupant is situated too close to the module housing, the discharge openings remain free and the gas bag unfolds neither at its full speed nor to its maximum hardness. Through this measure, occupants who are not optimally positioned are protected from the gas bag unfolding too aggressively.
As can be seen from the drawings of US 2004/0051286 A1, the gas bag module being described is particularly suitable for installation conditions in which the module opens towards the occupant and the gas bag unfolds as symmetrically as possible around the module. This typically applies to front passenger gas bags in the “mid-mount” position or driver's gas bags which are integrated in the steering wheel.
In the front passenger gas bags in the “top-mount” position (cf. FIG. 2) which are increasingly widespread nowadays, the described measurement of the distance between the module housing and the vehicle occupant is no longer possible in such a simple manner owing to the altered outlet position and the shape of the gas bag, and higher tolerances are involved. This can influence the reliability with which the discharge opening is closed or held open, according to the situation. In particular, occupants who are small, or child's seats which may be present are difficult to detect. In addition, it would be generally desirable to close the discharge opening on the module side not only on the basis of an optimum unfolding situation at a single point of the gas bag, namely the fastening point between the limiting strap and the gas bag wall, but on the basis of optimum unfolding possibilities of a determinative region of the gas bag.
It is therefore an object of the present invention to increase the sensitivity of a vehicle occupant restraint device with respect to an occupant who is not optimally positioned or with respect to a child's seat which is present during the unfolding process of the gas bag, and to reliably adapt the unfolding characteristic.